Drinking alcohol results in short-term behavioral changes and longer-term adaptations that lead to abuse and dependence. These adaptations are not understood, but a consensus suggests that, in accordance with the mechanism of all addictive drugs, an increase in the release of dopamine (DA) is associated with behavioral sensitization to alcohol and is related to the abuse liability of the drug. Although alcohol is known to enhance DA release in the nucleus accumbens (nAc), the mechanism is not known. In this proposal we will evaluate competing hypotheses for the action of alcohol on the DA system. The Specific Aims are: 1) to investigate the effects of alcohol on dopaminergic and GABAergic neurons in the VTA. The release of DA in the nucleus accumbens is activated by acute alcohol exposure in vivo. One possible explanation for this is that alcohol directly or indirectly increases the firing rate of DAergic neurons within the VTA, as is the case with other drugs of abuse, such as the opiates. We will investigate the effects of alcohol on identified populations of DAergic projection neurons and local GABAergic neurons in the VTA using GAD67-GFP and TH-GFP mice. The hypothesis to be tested is that acute alcohol activates the VTA, either by disinhibition (as with opiates) or by direct activation of DA neurons, which subsequently results in increased release of DA within the nAc. 2) To study the interactions between alcohol and dopamine release in the nucleus accumbens (nAc) We will use the newly developed technology of fluorescent false neurotransmitters (FFNs) to image individual DAergic terminals, and combined with the use of physiologically relevant stimulation parameters, compare these results with those using conventional cyclic voltammetry. The hypothesis to be tested is that alcohol increases DA release from a subset of DAergic neurons terminating within the nAc, possibly due to the differential presence of presynaptic GABAergic and/or cholinergic receptors. 3) To study the effects of alcohol on the activity of a population of cholinergic interneurons the in nAc and medium spiny neurons in the nAc. More than 90% of the cells in the ventral striatum are medium spiny neurons (MSNs), but several classes of interneurons also exist, including a population of cholinergic neurons, the activity of which strongly regulates evoked DA release in the nAc. The hypothesis to be tested is that alcohol enhances cholinergic neuron activity in the nAc.